This invention relates in general to making keys for rotary cylinder locks, and more particularly to a process and apparatus for making a plurality of different keys to open each lock in the same series, or sub-series, called "masterkeying".
A conventional rotary cylinder lock comprises an external portion of cylindrical cross-section, called "the cylinder", and a smaller internal, eccentrically-disposed cylinder called "the plug" having an inwardly projecting slot called "the keyway". Projecting normally into the keyway at spaced-apart positions along the axis of the plug are a series of "pin holes". The latter register with similar "pin holes" in the cylinder, each of which accomodates a small coil spring. Each of these springs presses against a plurality of aligned tumbler pins. When a key is pressed into the keyway, the lateral cuts or "bittings" in the key may function to seat in the bottom one of the aligned pins, raising the aligned pins up above what is called "the shear line", so that the interface between two pins coincides with the shear line, and the plug is disengaged from the cylinder and rotates to open the lock.
In accordance with prior art masterkeying practice, tumbler pins are interposed blindly into the small pin holes in the plug by guessing at the lengths of the pins needed to extend from the selected bitting of the key under test up to the shear line where the plug engages the internal surface of the cylinder. This process is cumbersome, and involves much time and patience, especially when there are three or four or more masterkeys which must be used to open a single lock, such as is the case in motels, hotels, apartment houses, public buildings, and public and private institutions.